Bug 142197

Description of problem:

Although the longterm goal of rpm is/was(??) to classify certain
actions which are currently done by %scriptlets, such a classification
will never cover all possible cases. Because it is easy for such
scriptlets to conflict with %_netsharedpath settings and the related
test is not trivial, a standardized test is highly needed. For samples
of broken scriptlets see the blocks-list of bug #51193.

My preferred solution would be a check like:

| %post
| <black_magic> /usr || exit 0     # check whether /usr is not in %_netsharedpath
| touch /usr/something


For '<black_magic>' you have the choice between

- a perl/awk/python/... script. Disadvantages are additional dependencies
  on perl/gawk/python (which might be superfluously on minimal systems),
  and the redundancy to write the same script into every %post

- a %macro executing the script; this removes the redundancy in the
  scripts but the superfluous dependencies remain. With recent rpm,
  such a macro can be provided in /etc/rpm/macros.netsharedpath from
  an additional package.

- a native C implementation of such a test; this can do simple pattern
  matching or use the related librpm function (I do not know if such a
  function exists). When linked against dietlibc, the pattern-matching
  thing will have nearly no dependency.

- a %macro executing the C program above. This avoids hardcoded paths
  in the scriptlet. I prefer this method.



Giving the actual value of %_netsharedpath to <black_magic> is a
problem: the direct execution of "rpm --eval '%{_netsharedpath}'" is
error-prone (how often have I to quote the '%'?) and incorrect as it
does not honor flags of current rpm invocation which might influence
%_netsharedpath (e.g. '--define _netsharedpath ...' or '--rcfile
%...').


Therefore, rpm would have to set an environment-variable like
'RPM_NETSHAREDPATH' before script-execution. Other interprocess
communication mechanisms like pipes or shared-memory are not
applicable (pipes must be open in scriptlet, but closed in started
programs) or too complicated (how will the shared-memory be
identified?).